Top- Based Adaptive Enumeration in Constraint Programming

Algorithm 5

:-lib(ic).

knight_tour(N, Board):-

 N2 is N*N,

 length(Board, N2),

 C = -2,-1,1,2,

 alldifferent(Board),

 ( fromto(Board, Q1|Cols, Cols, ), param(N,C) do

  t_Q2(Cols,Q2),

  I:: 1..N,

  J:: 1..N,

  A:: C,

  B:: C,

  IA #= I+A,

  JB #= J+B,

  IA #>= 1,

  JB #>= 1,

  IA #=< N,

  JB #=< N,

  abs(A)+abs(B) #= 3,

  (I-1)*N + J #= Q1,

  Q2 #= (I-1+A)*N + J+B

 ),

 % call to search predicate

t_Q2(A|B,A).

t_Q2(,A).